SMES coil configurations with reduced stray field

The stray field of SMES restricts its site location, although SMES has an attractive potential for power management and quality control. The stray field outside a solenoid is analyzed by a series of Legendre polynomials and the result is applied to the stray fields of various SMES coil configurations. As long as the summation of magnetic moments from all coils is zero, the term of a stray field decreasing as r/sub p//sup -3/ can be cancelled out. The higher order of the stray field can vanish if the coil arrangement is optimized. In this paper, the authors consider a single solenoid as a reference, active shield coils, axially displaced coils and multipole coils to reduce the stray field. The multipole coil configuration has high potential to drop the stray field, since the stray field behaves like r/sub p//sup (3+n/2)/, where n is the coil number.